This invention relates to a drawing or drafting roller arrangement for spinning machines, having at least three pairs of rollers forming successive drafting zones in the conveying direction of a sliver and having a device to stop the sliver that can be triggered by a disturbance and is assigned to the first pair of rollers.
Drafting roller arrangements having a device to stop the sliver are known, for example, from German Published Unexamined Application (DE-OS) No. 30 48 481. These arrangements are especially useful in the case of high working speeds and slivers of a relatively large cross section because otherwise there is a relatively high loss of fiber material during a disturbance, especially in the case of a yarn breakage. When the sliver is started again after the feeding is interrupted, difficulties may arise concerning a correct introduction of the sliver into the roller pairs. These difficulties occur especially in front of the last drafting zone since the sliver that, is generally guided freely there over a relatively large distance. In the subsequent main drafting zone, the sliver is, as a rule, guided by means of a belt support so that the entry into the last pair of rollers does not present any difficulties.
In order to avoid these difficulties in the case of a drafting roller arrangement having three pairs of rollers, it is known from German Published Unexamined Application (DE-OS) No. 31 00 049 to arrange a holding means for the sliver after the pair of entry rollers and in front of the second drafting zone, said holding means for the sliver being operated at the same time as the stopping device for the sliver and clamping in the sliver. The sliver will then tear only after or downstream of this holding means so that the position of the forming tuft or fiberbeard is defined. The purpose is that during the restarting process, when the holding means for the sliver is opened, the entry of the sliver into the pairs of rollers is improved.
The present invention is based on the objective of improving the uniformity of the drafting and thus the uniformity of the forming yarn in the case of a drafting roller arrangement of the initially mentioned type, without making the restarting of the sliver after a stop more difficult.
This objective is achieved according to the invention by providing that a sliver condenser is arranged upstream of the last drafting zone, said sliver condenser having guide surfaces tapering in the conveying direction of the sliver and being provided with a threading slot extending in the conveying direction of the sliver. The sliver condenser is held by means of a holding means in such a way that it can be moved out of the drafting zone, transversely to the conveying direction, in the direction of the side facing away from the threading slot.
Especially in the case of slivers with a relatively large cross section, the sliver condenser makes the drawing of the yarn significantly uniform. However, the difficulty arises that the sliver does not enter into the condenser or enters only with great difficulty into the condenser when the sliver feeding device is turned on again, but rather bunches up in the area of the sliver condenser. In order to avoid this difficulty, it is provided that the sliver condenser, during the reentry of the sliver into the last drafting zone, is moved out of the activity range of the drafting zone. It will be returned to the sliver and will resume its function only when the entry of the sliver into the last drafting zone has been completed.
The use of sliver condensers in the case of drafting roller arrangements is known from German Published Unexamined Application (DE-OS) No. 30 21 632, where, however, these drafting roller arrangements are not provided with a stopping device for the sliver so that in the case of this construction, the problems caused by such a stopping device do not occur.
According to the invention, it is provided that the sliver condenser is selectively movable out of its operating position against a restoring force. The operator must therefore operate the sliver condenser only at the beginning of the restarting of the sliver, said condenser then automatically returning into its operational position. It is therefore not possible for the operator to forget to return the sliver condenser to its operating position.
In order to obtain uniform operating conditions, it is provided in a further development of the invention that the sliver condenser, in the operating position, rests against a stop.
In a further development of the invention, it is provided that the sliver condenser is mounted at a holding means so that it can be detached easily. It therefore becomes possible to exchange the sliver condenser guide in a simple matter in the case of wear or in the case of a change of the fiber materials to be processed.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.